number of square miles each. The surface resembles a newly-planted cornfield, being covered with little mounds of earth, each indicating the home of a family. On each mound sits a prairie dog on his haunches, like a kangaroo, and greets the intruder with a chorus of short piping barks. They are shy little fellows, and, on a nearer approach, they make a dive for their holes, and, with a short quick wriggle of their hinder parts, disappear.

Living with them in their villages, and tolerated perforce, are rattlesnakes (Crotalus), and a small species of owls who make a good diet off the young of their hosts.

7. Geology of the Great Plains.

From Archæan time to the end of the Cretaceous period this was a region of deep seas. In early Palæozoic time it was covered by the ocean that spread continuously over almost the entire region of the United States. Its expanse was interrupted only by a few islands in the region of the Rocky Mountains, and a few embryonic mountain ridges in the Appalachian region.

In Mesozoic time the "Plains were covered by the great Mediterranean Sea, which extended from the Gulf of Mexico to the Arctic Ocean. In Tertiary time the surface was marked by a series of great fresh-water basins. The fauna and flora of the lake deposits of the plains are of the same age as those on the west side of the Rocky Mountains. During the Middle Tertiary the continental surfaces were broad and covered with a vegetation very much like that of the present day, although the climate was much milder than now. Over the western plains "roved great herds of quadrupeds, rivalling in number and variety those that have struck with wonder and surprise the traveller in South Africa." The following picture of North America during the Tertiary age is drawn by Pro

fessor Newberry in Hayden's Annual Report for 1870"Then a warm and genial climate prevailed from the Gulf to the Arctic Sea; the Canadian highlands were higher, but the Rocky Mountains lower and less broad. Most of the continent exhibited an undulating surface, rounded hills and broad valleys covered with forests grander than any of the present day, or wide expanses of rich savannah, over which roamed countless herds of animals, many of gigantic size, of which our present meagre fauna retains but a few dwarfed representatives. Noble rivers flowed through plains and valleys, and sea-like lakes, broader and more numerous than those the continent now bears, diversified the scenery. Through unnumbered ages the seasons ran their ceaseless course, the sun rose and set, moons waxed and waned over this fair land; but no human eye was there to mark its beauty, nor human intellect to control and use its exuberant fertility. Flowers opened their many-coloured petals on meadow and hillside, and filled the air with their perfumes, but only for the delectation of the wandering bee. Fruits ripened in the sun, but there was no hand there to pluck, nor any speaking tongue to taste. Birds sang in the trees, but for no ears but their own. The surface of lake or river was whitened by no sail, nor furrowed by any prow but the breast of the water-fowl; and the far-reaching shores echoed no sound. but the dash of the waves and the lowing of the herds that slaked their thirst in the crystal waters.

"Life and beauty were everywhere, and man, the great destroyer, had not yet come; but not all was peace and harmony in this Arcadia. The forces of nature are always at war, and redundant life compels abundant death. The innumerable species of animals and plants had each its hereditary enemy, and the struggle of life was so sharp and bitter that in the lapse of ages many genera and species were blotted out for ever.

"The herds of herbivores-which included all the genera now living on the earth's surface, with many strange forms long since extinct-formed the prey of carnivores commensurate to these in power and numbers. The coo of the dove and the whistle of the quail were answered by the scream of the eagle, and the lowing of herds and the bleating of flocks come to the ear of the imagination mingled with the roar of the lion, the howl of the wolf, and the despairing cry of the victim. Yielding to the slow-acting but irresistible forces of nature, each in succession of these various animal forms has disappeared, till all have passed away or been changed to their modern representatives; while the country they inhabited, by the upheaval of its mountains, the deepening of its valleys, the filling and draining of its great lakes, has become what it is."